The use of photopolymerizable compositions for the production of images by information-wise exposure thereof to actinic radiation is well known. Several methods for forming images using photopolymerizable compositions are known. All these methods are based on the principle of introducing a differentiation in properties between the exposed and non-exposed parts of the photopolymerizable composition e.g. a difference in solubility, adhesion, conductivity, refractive index, tackiness, permeability, diffusibility of incorporated substances e.g. dyes etc . . . The thus produced differences may be subsequently employed in a developing step to produce a visible image and/or master for printing e.g. a lithographic or electrostatic printing master.
A difference in solubility between the exposed and non-exposed parts of the photopolymerizable composition is often used for the production of lithographic printing plates where a hydrophilic base is coated with the photopolymerizable composition, subsequently exposed and developed using a solvent to remove the non-exposed or insufficiently exposed parts. Such a process is for example described in "Unconventional imaging processes" by E. Brinckman, G. Delzenne, A. Poot and J. Willems, Focal Press London-New York, first edition 1978, pages 33 to 39.
The use of the difference in tackiness to obtain an image is described in e.g. U.S. Pat. Nos. 3,060,024, 3,085,488 and 3,649,268. According to the method disclosed in these U.S. patent applications the image-wise exposed photopolymerizable composition looses its tackiness in the exposed parts while the non-exposed parts keep their tackiness. The non-exposed parts can therefore be colored with dry dye pigments to make the image visible.
According to the methods described in e.g. U.S. Pat. No. 3,245,796 and EP-A 362,827 the diffusibility of a dye is impeded in the photo-exposed parts of the photopolymerizable composition so that during an overall thermal heating subsequent to photo-exposure dye substances in the non-exposed areas will be able to diffuse to a receptor material. According to a similar method described in U.S. Pat. No. 4,587,198 the photopolymerizable composition is made impermeable in the exposed parts for a sublimable dye or dye-pigment present in a layer adjacent to the layer comprising the photopolymerizable composition.
According to a method disclosed in U.S. Pat. No. 3,060,023 the adhesion of the photopolymerizable composition is modified upon image-wise exposure. After image-wise exposure the non-exposed parts will stick or adhere, during a step of overall heating, to a receiving sheet thus allowing the transfer of the non-exposed parts to the receiving sheet.
In EP-A-502562 there are disclosed urethane type multi functional monomers for use in an imaging element. The disclosed imaging element is of high speed and the obtained images are of high quality. However it is desirable to further improve the speed of these imaging elements especially when the imaging elements are to be used in thermal transfer processing.